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Feeds for Dairy Cows

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Babcock Institute for International
Dairy Research and Development
Dairy
Essentials
University of Wisconsin-Madison
6) FEEDS FOR DAIRY COWS
Michel A. Wattiaux
Babcock Institute
W. Terry Howard
Department of Dairy Science
INTRODUCTION
In general, feeds are classified into one of
the following categories:
• Forages;
• Concentrates (energy and protein feeds);
• Minerals and vitamins.
This classification is a convenient way to
group feeds, but it is somewhat arbitrary.
Classifying feeds is not as important as
knowing which feeds are available, their
nutritive value, and the factors that affect
their utilization in a ration.
FORAGES
In general, forages are the vegetative
parts of grasses or legume plants containing
a high proportion of fiber (more than 30%
neutral detergent fiber). They are required
in the diet in a coarse physical form
(particles with a length of more than 2.5
cm) to help rumen function.
Usually, forages are grown on the farm.
They may be grazed directly or harvested
and preserved as hay or silage. Depending
on the cow's stage of lactation, they should
contribute from almost 100% (for nonlactating cows) to no less than 35% (for
cows in early lactation) of the ration dry
matter. The general characteristics of
forages are as follows:
• Bulky: Bulkiness puts limits on how
much a cow can eat. The energy
intake and the milk production of a
cow may be limited by too much
forage in a ration. However, bulky
feeds are essential to stimulate
rumination and maintain the health of
the cow.
• High Fiber and Low Energy: Forages
may contain from 30 to 90% fiber
(neutral detergent fiber). In general,
the higher the fiber in a forage, the
lower the energy content of the forage.
• Variable in Protein: Depending on
the stage of maturity, legumes may
contain 15 to 23% crude protein;
grasses typically contain 8 to 18%
crude protein (depending on the level
of nitrogen fertilization), and crop
residues may have only 3 to 4% crude
protein (straw).
From a nutritional standpoint, forages may
range from very good feeds (lush young
grass, legumes at a vegetative stage of
maturity) to very poor feeds (straw,
browse).
Grasses and Legumes
High quality forage can make up twothirds of the ration dry matter with cows
eating 2.5 to 3% of their body weight as
forage dry matter (for example, a cow of
600 kg, can eat 15 to 18 kg dry matter of
good quality forage). Cows usually eat
more legumes than grasses at similar stages
of maturity. However, good quality
forages fed in balanced diets will supply
much of the protein and energy needed for
milk production.
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21
Dairy Essentials – Nutrition and Feeding
Soil and climate conditions usually
determine the type of forage that is most
commonly grown in a region. Both grasses
(rye-grass, brome grass, bermuda grass,
fescue, orchard grass) and legumes (alfalfa,
clover, lespedeza, birdsfoot trefoil) are
widely spread throughout the world.
Grasses need nitrogen fertilizers and
moisture conditions to grow well.
However, legumes are more resistant to
drought. Also, they can add as many as 200
kg of nitrogen/year/hectare in the soil
because they live in association with
bacteria that convert nitrogen of the air into
nitrogen fertilizer.
The feeding value of forages is greatly
influenced by the growth stage when
harvested or grazed. Growth can be
divided in three successive stages:
1) Vegetative stage;
2) Flowering stage;
3) Seed formation stage.
Usually, the feeding value of a forage is
the highest during vegetative growth and
the lowest during the seed formation stage.
With advancing maturity, the concentration
in protein, energy, calcium, phosphorus,
and digestible dry matter in the plant
decreases while the fiber concentration
increases. As fiber increases, the lignin
content within the fiber also increases.
Lignin is indigestible and makes the
carbohydrates in the fiber less available to
ruminal microbes. As a result the energy
value of the forage decreases.
Thus, when forages are grown with the
purpose of feeding cattle they should be
harvested or grazed at an early stage of
maturity. Corn (maize) and sorghum
harvested as silage are exceptions because,
despite the decrease in nutritive value of
the vegetative parts of the plants (stem and
leaves) during seed formation, a large
amount of highly digestible starch
accumulates in the grains.
The maximum yield of digestible dry
matter of a forage crop is obtained:
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• At the late boot to early head stage of
maturity for grasses;
• At the mid-to-late bud stage of
maturity for legumes;
• Before the grains are fully dented for
corn and sorghum.
There is little that can be done to prevent
the loss of nutritive value of a forage with
advanced maturity. For each day of
delayed harvest after the optimum stage of
maturity, the potential milk production of
cows eating the forage will be penalized.
However, various strategies can be used to
maintain the availability of forage that has
good nutritive value:
1) Develop a grazing strategy that
matches the number of animals in a
pasture with the rate of growth of the
grass;
2) Plant a mixture of grasses and legumes
that have different rates of growth and
maturity throughout the season;
3) Harvest at an early stage of maturity
and preserve as either hay or silage;
4) Feed lower quality forage to the dry
cows or the cows in late lactation and
the good quality forage to the cows in
early lactation.
Crop residues and industrial byproducts of poor feeding value
Crop residues are the parts of the plants
that remain in the field after harvesting the
primary crop (e.g., corn stover, cereal straw,
sugar cane bagasse, peanut hay). Crop
residues may be grazed, processed as dry
feed, or made into silage. Some general
characteristics of most crop residues are:
• Inexpensive bulk feed;
• High in indigestible fiber because of
high lignin content (chemical
treatments can be used to upgrade
their feeding value);
• Poor in crude protein;
• Need to be supplemented properly,
especially in protein and minerals;
The Babcock Institute
6 - Feeds for Dairy Cows
• Need to be coarsely chopped when
harvested or at feeding time;
• Should be included in ration of nonlactating animals with low energy
requirements.
concentrates are important feeds that allow
for formulating diets that will maximize
milk production. In general, the maximum
amount of concentrates a cow can receive
per day should not exceed 12 to 14 kg.
CONCENTRATES
Examples of Concentrates
• Cereal grains (barley, corn,
sorghum, rice, wheat) are the typical "high
energy" feeds for dairy cows, but they are
low in protein. Rolled or cracked cereal
grains are excellent sources of readily
fermentable carbohydrates (starch) which
increase the concentration of energy when
included in the diet. However, too much
cereal grain in the diet (more than 10 to 12
kg/cow/day) reduces chewing activity,
proper rumen function, and lowers milk fat
percentage.
The various industrial treatments of cereal
grain results in numerous cereal byproducts having extremely variable
nutritive value:
• Corn gluten meal is obtained from
the wet milling of corn starch. It is a an
excellent source of protein (40 to 60%) and
energy. Corn gluten feed, another byproduct of starch production, contains less
protein and more fiber. Brans of cereal
grains (rice, wheat) add bulk and fiber to a
diet and contain from 14 to 17% protein.
Wheat bran is a good source of phosphorus
and functions as a laxative. Hulls are the
outer covering of some cereal grains
(barley, oats, rice) that contain only 3 to 4%
protein but 85 to 90% of highly indigestible
fiber.
• Brewing and distilling by-products
of cereal grains are good sources of slowly
digestible carbohydrates and protein (20 to
30%). Malt sprouts (radicles from
germinating barley) have a bitter taste and
are usually mixed with other feeds.
• Roots and tubers (carrots, cassava,
beets, potatoes, turnips) are usually
palatable, good sources of readily
fermentable carbohydrates (energy), but
low in protein (less than 10%).
There is no good definition for the word
concentrate.
However, they may be
described by their characteristics as feeds
and their effect on rumen function.
Usually, concentrates have the following
characteristics:
• They are low in fiber and high in
energy.
• They can be either low or high in
protein. Cereal grains contain <12%
crude protein, but oilseed meals
(soybean, cotton, peanut), referred to
as protein feeds, can contain > 50%
crude protein.
• They have a high palatability and are
usually eaten rapidly. As opposed to
forage, concentrates are feed that
usually have a low volume per unit of
weight (high specific gravity).
• As opposed to forages, they do not
stimulate rumination.
• They usually ferment faster than
forages in the rumen and they
increase the acidity (reduce the pH) of
ruminal contents which may impede
normal fiber fermentation.
• When they comprise more than 60 to
70% of a ration, they may cause health
problems.
Dairy cows with high genetic potential for
milk production also have high
requirements for energy and protein.
Given that cows can eat only a certain
amount per day, forage alone cannot
supply the required amount of energy and
protein. Generally, the purpose of adding
concentrates to the ration of dairy cattle is
to provide a concentrated source of energy
or protein to supplement the forage and
meet the animal requirements. Thus,
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23
Dairy Essentials – Nutrition and Feeding
• By-products of the sugar industry
(molasses, sugar beet pulp) are usually high
in digestible fiber (beet pulp) or simple
sugars (molasses) which make them very
palatable feeds.
• Certain plants contain a high
concentration of lipids in their seed
(oilseeds). Many of them grow in the
tropics and subtropics (soybean,
groundnut, cotton), but some grow in
temperate climates (linseed [flax], canola
[rapeseed], and sunflower). Intact oilseeds
can be used as high energy feeds, but they
usually contain anti-nutritional substances.
Oilseed meals obtained after the extraction
of the oil from oilseeds, contain from 30 to
50% protein and are used as typical
"protein feeds" for dairy cows (e.g., soybean
meal).
• Seeds of legumes (beans, chickpeas,
cowpeas) contain anti-nutritional
substances, but after proper processing, are
good energy and protein sources.
• Proteins of animal origin (meat and
bone meal, feather meal, fish meal) are
usually resistant to ruminal degradation,
and may be good sources of calcium and
phosphorus. They need to be handled
properly to avoid the risk of bacterial
infections. Whey, a byproduct of dairy
processing, contains large amounts of milk
sugar (lactose) and some proteins and
minerals. However, those nutrients may be
very dilute when the whey is not dried.
MINERALS AND VITAMINS
Minerals and vitamins are of great
importance in nutrition. For example, milk
fever in early lactation is due to an
imbalance in calcium metabolism, and
phosphorus is essential for high herd
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fertility. Deficiencies may result in large
economic losses. In lactating dairy cows,
the macro-minerals of concern are sodium
chloride (NaCl), calcium (Ca), phosphorus
(P), and sometimes potassium (K),
magnesium (Mg) and sulfur (S). Also, most
micro minerals (e.g., iodine, selenium) are
required to achieve optimal production and
reproduction. The small amount of microminerals usually required in a dairy ration
is often included as a premix in the
concentrates or as fortified salt.
All feeds, except urea and fat, contain at
least limited amounts of minerals. Because
legumes contain more calcium than grasses,
diets based on legumes will require less
calcium supplementation. Molasses is rich
in calcium and animal protein by-products
containing bones are good sources of
calcium and phosphorus. Salt (sodium
chloride) is a mineral supplement that can
be offered free-choice. A mineral mix
containing calcium, phosphorus, or both
(e.g., dicalcium phosphate) may be required
depending on the ingredients in the ration.
Green forages usually contain low levels of
phosphorus relative to the cow's needs.
Corn [maize] silage contains little calcium
and phosphorus and both minerals are
required in the mineral supplement mix.
The amount of mineral mix required in the
diet usually ranges from 0 to about 150
g/cow/day.
Vitamin A, D, and E are of concern, with
vitamin A the most likely to be deficient in
areas with long winters or long dry seasons.
Rumen microbes synthesize B complex
vitamins, vitamin C, and vitamin K, so
these vitamins are not usually required in
the diet.
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